The propagation of inverted Neel wall sections instead of magnetic bubbles in a serial access memory system was proposed by L. J. Schwee in the publication "Proposal On Cross-Tie Wall and Bloch-line Propagation In Thin Magnetic Films," IEEE Transactions on Magnetics, MAG 8, No. 3, pages 405-407, September 1972. Such a memory system utilizes a ferromagnetic film of 81% Ni-19% Fe of approximately 350 Angstroms (A) thick in which cross-tie walls can be changed to Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate fields. Associated with the cross-tie walls is a section of inverted Neel wall that is bounded by a cross-tie on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered at one end of the serial access memory system by the generation of an inverted Neel wall section bounded by a cross-tie on one side and a Bloch-line on the other side that is representative of a stored binary 1 and a non-inverted Neel wall section, i.e., the absence of a cross-tie and Bloch-line pair that is representative of a stored binary 0, and is moved or propagated along the cross-tie wall by the successive generation and then the selective annihilation of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the D. S. Lo, et al., U.S. Pat. No. 3,906,466 there is disclosed a propagation circuit for the transfer of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the L. J. Schwee U.S. Pat. No. 3,868,660 and in the publication "Cross-tie Memory Simplified By The Use of Serrated Strips," L. J. Schwee, et al., AIP Conference Proceedings, No. 29, 21st Annual Conference On Magnetism and Magnetic Materials, 1975, published April 1976, pages 624-625 there have been published some more recent results of the further development of cross-tie wall memory systems.
In prior art cross-tie wall memory systems, the magnetic film that functions as the storage medium has the property of uniaxial anisotropy provided by its easy axis induced magnetic fields, which easy axis is generated in the magnetic film during its generation in the vapor deposition process. This easy axis provides a magnetic field induced anisotropy which constrains the generation of the cross-tie wall along and parallel to the easy axis. In the above L. J. Schwee, et al., publication there are proposed serrated strips of Permalloy film, about 350 Angstroms (A) in thickness and 10 microns (.mu.) in width, each of which serrated strips is etched from a planar layer of the magnetic material so that the geometric centerline of the strip is aligned along the easy axis of the film. After an external magnetic field is applied normal to the strip length, i.e., transverse the easy axis or geometric centerline of the film, the magnetization along the opposing serrated edges rotates back to the nearest direction that is parallel to the edge. This generates two large domains that are separated by a domain wall, or cross-tie wall, that is formed along the centerline of the strip. Cross-ties are formed at the necks of the serrated edges while Bloch-lines are formed in the potential wells between adjacent necks.
This serrated strip configuration, because of the contour of the opposing edges of the strip, provides the means whereby the cross-tie, Bloch-line pairs are structured at predetermined memory sections along the strip. However, because the serrated strips have M induced anisotropy incorporated into the film during deposition, such strips cannnot be utilized to permit the use of nonlinear, i.e., curved, data tracks, which curved data tracks are essential to the configuration of cross-tie wall memory systems of large capacity or of digital logic function capabilities. Accordingly, it is desirable that there be provided a means whereby cross-tie wall memory systems use nonlinear, i.e., curved, data tracks to achieve the desirable characteristics of single wall, e.g., bubble, domain memory systems, such as those of the A. H. Bobeck U.S. Pat. No. 3,729,726 and the D. M. Heinz U.S. Pat. No. 3,735,145, in cross-tie wall memory systems.